A tomographic study of the lithosphere beneath the Pyrenees from local and teleseismic data

American Geophysical Union (AGU) - Tập 100 Số B9 - Trang 18117-18134 - 1995
Annie Souriau, M. Granet

Tóm tắt

A tomographic image of the Pyrenean lithosphere from the surface down to 200 km is deduced from the propagation of the seismic waves recorded at the regional Pyrenean seismograph network. Crustal and subcrustal models are derived independently from the inversion of two different data sets. P and S velocity models for the crust are obtained from the propagation of local earthquakes. The upper crust appears very heterogeneous and exhibits sharp velocity contrasts. In the uppermost 7 km, an east‐west trending zone with velocities up to 6% higher than the surrounding material is observed all along the Pyrenees. This zone coincides in most places with the exposure of the Paleozoic rocks of the Axial Zone. Low velocities are observed on both sides of this high‐velocity zone. At the surface, they coincide with well‐known sedimentary basins but dip down to about 11 km depth toward the axis of the range. In the central and eastern Pyrenees, two large, high‐velocity bodies stand out in the North Pyrenean Zone and extend down to the base of the upper crust. They coincide with large positive gravity anomalies and are interpreted as lower crust or upper mantle blocks uplifted into the upper crust. The lower crust is poorly resolved but appears to be less heterogeneous than the upper crust. Moreover, the lower crustal structure is almost uncorrelated with the upper crustal structure. The major feature of the lower crust is a low‐velocity anomaly which stretches along the North Pyrenean Fault in the western Pyrenees and beneath the Axial Zone in the central Pyrenees; its location nearly coincides with the distribution of the seismicity. In the upper mantle, P models are derived from the travel times of the remote events recorded at the Pyrenean stations. The most important feature is the presence, in the eastern and central Pyrenees, of a vertical, low‐velocity heterogeneity south of the North Pyrenean Fault down to 80–100 km. This structure exhibits a 2% velocity contrast with respect to the surrounding structures and is interpreted as lower crustal material subducted during the Pyrenean convergence. This heterogeneity is not observed in the western Pyrenees, suggesting that the crustal shortening has been completely accommodated by several thrusts in the thinned Aquitaine crust.

Từ khóa


Tài liệu tham khảo

10.1029/JB082i002p00277

10.2113/gssgfbull.S7-XX.5.681

10.1111/j.1365-246X.1994.tb03295.x

10.1016/0012-821X(77)90038-3

10.1029/90JB00482

Choukroune P., 1992, Tectonic evolution of the Pyrénées, Annu. Rev. Earth Planet. Sci., 20, 143, 10.1146/annurev.ea.20.050192.001043

10.2113/gssgfbull.S7-XX.5.689

10.1029/TC008i001p00023

Daignières M. Les Pyrénées' Une chaine intracontinentale sur un grand décrochement? Eléments de réponse géophysique thesis Univ. Montpellier France 1982.

Daignières M., 1981, Lateral variation of the crust in the North‐Pyrenean Zone, Ann. Géophys., 37, 435

10.1016/0012-821X(82)90175-3

10.1029/TC008i005p01051

Daigniéres M., 1994, The Arzacq‐Western Pyrénées ECORS deep seismic profile, Publ. Eur. Assoc. Pet. Géol., Mem., 4, 199

deCabissole B. Apport des données gravimétriques à la connaissance de la chaîne des Pyrénées le long du profil ECORS thesis 186 pp. Univ. Montpellier France 1989.

Eberhart‐Phillips D., 1986, Three‐dimensional velocity structure in Northern California Coast Ranges from inversion of local earthquake arrival times, Bull. Seismol. Soc. Am., 76, 1025

Gagnepain J., 1980, Sismicité de la région d'Arette (Pyrénées Atlantiques) et mécanismes au foyer, Ann. Géophys., 36, 499

Gagnepain‐Beyneix J., 1985, Variation of source parameters of small western Pyrenean earthquakes and their relation to main shock occurrence, Ann. Geophys., 3, 381

Gallart J., 1980, The Eastern Pyrenean domain: Lateral variations at crust‐mantle level, Ann. Geophys., 36, 141

Gallart J., 1981, Crustal structure of the Paleozoic Axial Zone of the Pyrénées and transition to the North Pyrenean Zone, Ann. Geophys., 37, 457

10.2113/gssgfbull.S7-XXIV.2.293

10.1016/0012-821X(88)90032-5

10.1016/0040-1951(86)90256-8

Grandjean J. Mise en evidence des structures crustales dans une portion de charlie et de leur relation avec les bassins sédimentaires; application aux Pyrénées occidentales au travers du projet ECORS Arzacq‐Pyrénées thesis Univ. Montpellier France 1992.

10.1016/0031-9201(88)90034-9

10.1111/j.1365-246X.1995.tb03509.x

Grasso J. R., 1990, Ten years of seismic monitoring over a gas field, Bull. Seismol. Soc. Am., 80, 450

Herrin E., 1968, Seismological tables for P phases, Bull. Seismol. Soc. Am., 58, 1193, 10.1785/BSSA0580041193

Hirn A., 1973, Long range profiles in Western Europe, II, Fine structure of the lower lithosphere in France (southern Bretagne), Z. Geophys., 39, 363

10.1029/GL007i004p00263

10.1038/308531a0

Jeffreys H., 1940, Seismological Tables

Klein F. W. Hypocenter location program HYPOINVERSE Part 1 Users guide to versions 1 2 3 and 4U.S. Géol. Sur. Open file report 78‐694 1978.

Le Pichon X., 1970, La Faille Nord‐pyrénéenne: Faille transformante liée à l'ouverture du Golfe de Gascogne, C.R. Acad. Sci. Paris, Sér. D, 271, 1941

10.1016/0040-1951(90)90443-C

Mattauer M., 1968, Les traits structuraux essentiels de la chaine pyreneenne, Rev. Geogr. Phys. Géol. Dyn., 10, 3

Mattauer M., 1985, Présentation d'un modele lithosphérique de la chaîne des Pyrénées, C. R. Acad. Sci. Paris, Sér. II, 300, 71

10.2113/gssgfbull.VI.2.307

10.1016/0012-821X(68)90094-0

Monchoux P., 1971, Comparaison et classement des massifs de lherzolithe de la zone mesozoique nord‐pyreneenne, Bull. Soc. Hist. Nat. Toulouse, 107, 393

10.1007/978-94-011-3066-0_21

10.1016/0040-1951(92)90362-A

10.1016/0040-1951(86)90262-3

Olivet J. L. J.Bonnin P.Beuzart J. M.Auzende Cinematique de l'Atlantique Nord et Central Rapp. Sci. Tech54 108Publ. Cen. National Exploit. Oceans 1984.

Poupinet G., 1989, A seismological platform transmitting via Meteosat, Bull. Seismol. Soc. Am., 79, 1651, 10.1785/BSSA0790051651

10.1130/0091-7613(1992)020<0157:COTLSB>2.3.CO;2

10.1111/j.1365-246X.1995.tb06436.x

10.1130/0091-7613(1991)019<0613:KOTPBB>2.3.CO;2

10.1029/TC008i001p00041

10.1016/0040-1951(88)90284-3

10.1016/0040-1951(86)90258-1

10.1016/0040-1951(92)90065-E

10.1130/0091-7613(1991)019<0522:TJOBOB>2.3.CO;2

Souquet P., 1976, Nouvelle hypothèse sur la formation des Pyrénées, C.R. Acad. Sci. Paris, Sér. D, 282, 2139

Souquet P., 1987, Allochtonie des Massifs primaires Nordpyrénéens des Pyrénées centrales, C. R. Acad. Sc. Paris, Sér. II, 305, 733

Souriau A., 1980, The crust and upper mantle beneath the Pyrénées, from surface waves: Tectonic implications, Ann. Geophys., 36, 159

10.1029/JB088iB10p08226

10.1016/0040-1951(89)90039-5

10.1029/JB078i023p05118

10.1016/0012-821X(84)90041-4

Thông tin
Thông tin xuất bản

American Geophysical Union (AGU)

Tập 100 Số B9

18117-18134

Thông tin tác giả